The long range goal of this program is the development of a self-contained, implantable, electrochemical device, capable of continuously monitoring the glucose level of the interstitial fluid. The operation of this device will be based upon the electrooxidation of glucose at a metallic electrode such as platinum to produce currents that are related to the concentration of glucose. Platinum has been tentatively selected as the electrode material of choice, because considerable evidence has already been obtained that it can be expected to exhibit excellent stability under in-vivo conditions. All work is being performed in either Krebs-Ringer based solutions (t equals 37 degrees C, pH-7.4), and natural or synthetic serum ultrafiltrate. Since materials in the interstitial fluid other than glucose can also exhibit electroactivity, either by inhibition of glucose electrooxidation and/or by themselves being oxidized, work is now in progress to determine the effects of these coreactants and inhibitors on the glucose electrode response. It has already been determined that although chloride is a strong inhibitor, that for chloride variations within the physiologic range, that little effect is noted on the rate of glucose electrooxidation. Changes in the oxygen partial pressure from 0 to 100 mm of Hg and changes in pH from about 7 to 7.8 have also been found to exert only a small effect on the glucose current. Urea is a strong inhibitor at some potentials and can itself be oxidized at other potentials. Nevertheless, methods have been developed for unambiguously determining glucose for urea variations ranging from 20 to 200 mg/dl. Amino acids exhibit electrochemical behavior similar to urea. Work is now being directed towards developing methods for determining glucose in the presence of varying concentrations of such amino acids.